A61F2/446—Joints for the spine, e.g. vertebrae, spinal discs for the fusion of spinal bodies, e.g. intervertebral fusion of adjacent spinal bodies, e.g. fusion cages having a circular or elliptical cross-section substantially parallel to the axis of the spine, e.g. cylinders or frustocones

A61F2/4465—Joints for the spine, e.g. vertebrae, spinal discs for the fusion of spinal bodies, e.g. intervertebral fusion of adjacent spinal bodies, e.g. fusion cages having a circular or kidney shaped cross-section substantially perpendicular to the axis of the spine

A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents

A61F2/02—Prostheses implantable into the body

A61F2/30—Joints

A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof

A61F2002/30316—The prosthesis having different structural features at different locations within the same prosthesis; Connections between prosthetic parts; Special structural features of bone or joint prostheses not otherwise provided for

A61F2002/30383—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements made by laterally inserting a protrusion, e.g. a rib into a complementarily-shaped groove

A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents

A61F2/02—Prostheses implantable into the body

A61F2/30—Joints

A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof

A61F2002/30316—The prosthesis having different structural features at different locations within the same prosthesis; Connections between prosthetic parts; Special structural features of bone or joint prostheses not otherwise provided for

A61F2002/30535—Special structural features of bone or joint prostheses not otherwise provided for

A61F2002/30604—Special structural features of bone or joint prostheses not otherwise provided for modular

A61F2250/00—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof

A61F2250/0014—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof having different values of a given property or geometrical feature, e.g. mechanical property or material property, at different locations within the same prosthesis

A61F2250/0028—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof having different values of a given property or geometrical feature, e.g. mechanical property or material property, at different locations within the same prosthesis differing in fibre orientations

Abstract

The cylindrical fiber reinforced implant (1) is designed to be
inserted between two adjacent vertebrae. The implant having an outer
wall (2) with a general cylindrical or oval shape and preferably an open
volume for bone filling. Said wall (2) having reinforcing fibers (12,17)
which at least in part are oriented in a first direction. A support (6)
extending within said volume having reinforcing fibers (10,11) which are
at least in part oriented in a second direction, said first and said
second directions are different. Preferably the fibers (12,17) of the
outer wall (2) are at least partly concentrically oriented. The support
(6) is preferably a separately formed part, that is inserted into the
outer wall.

Description

[0001]

The present invention relates to a three-dimensional fiber reinforced
implant, particularly a vertebral cage designed to be inserted
between two adjacent vertebra according to the preamble
of claim 1.

[0002]

Fiber reinforced implants are well known. US 5,429,863 for example
discloses a vertebral implant cage, that is fabricated from
a block, which is a fiber reinforced composite structure. Carbon
fibers are located in every part of the block and randomly interlocked.
The cage may have the shape of a cylindrical rod and
is provided with cavities which are filled with bone material
and is designed to be inserted between adjacent vertebrae.

[0003]

US 5,906,616 discloses a conically-shaped fusion cage provided
with a thread formed as a part of an external conical surface.
Apertures provide for bone growth between the engaged vertical
bone and bone material packed within the cage.

[0004]

US 5,968,098 discloses a fusion cage having a generally elliptical
cross-section. It includes an entry end portion, a trailing
end portion and a thread as a part of an external conical surface.
The cage is preloaded with bone material and inserted into
the desired surgical location with well known surgical instruments.

[0005]

A fusion cage formed of radiolucent material is also disclosed
in EP-A- 0 307 241. The cage has a roughened outer surface for
receiving bone in-growth and end faces with means securing it on
a tool for insertion on the desired site of the vertebrae.

[0006]

The role of a vertebral implant is to stabilize a vertebral segment
and to bear load while the surrounding bone consolidates,
taking over the mechanical function with a viable bone fusion.
On one hand the implant must be robust enough to bear rotation
at insertion, and axial load, sheer and fatigue during weight
bearing. On the other, the implant must provide enough space for
bone graft to grow through or around the device. Thus cage designers
are faced with a trade off what makes the implant bear
load, and the bone ports which must carry enough bone tissue required
for bone consolidation. Furthermore, it has been postulated
that stress shielding in an implant may prevent fusion of
viable bone through the implant, and strength and stiffness
should be as close to the surrounding bone tissue as possible.

[0007]

Several materials are used for inter-body cages and most commonly
are Titanium Alloy, PEEK as well as carbon composite. Titanium,
while certainly strong enough for the application, has
the disadvantage of being a radiographically opaque, making it
impossible to visualize if bone has grown through the cage with
standard x-ray. It is also known that titanium also produces artificiats
for other radiographic examinations such as C.T. or
MRI.

[0008]

It is an objective of the present invention to provide a three-dimensional
fiber reinforced implant, that is radiolucent and
provides increased mechanical performance, while at the same
time maximizes the space for bone graft.

[0009]

Cylindrical implants have the advantage of easier insertion.Both
the reaming and interspace preparation and cage insertion are
performed with a twisting motion.

[0010]

Square or rectangular cages, on the other hand, can be more easily
reinforced with vertical struts. To prevent collapse of cylindrical
cages, wall thickness is increased that reduces cavity
size preventing the formation of viable bone. The invention described
herein, through the use of selectively orienting the fibers
in the various cage components has contributed a cage resistant
to collapse and rotation, but preserves an ample cavity
for bone.

[0011]

The implant according to the present invention is provided with
a support extending within the outer wall and has reinforcing
fibers which are at least in part oriented in a direction which
is different to the orientation of fibers embedded into the
outer wall. The additional orientation of the fibers within the
support prevents a deformation of the implant to where the fibers
of the outer wall are bent beyond the point of failure. Deformation
beyond the point of breakage is prevented in axial
load, bending, rotation, impact and shear.

[0012]

The support is preferably a separately formed part, that is inserted
into the outer wall, but can be also a part of the outer
wall.

[0013]

Other advantages and features of the present invention will be
apparent to those skilled in the art after reading the following
specification with reference to the accompanying drawings.

Fig. 1

is a schematic perspective view of a fiber reinforced
cage of this invention,

Fig. 2

is a schematic perspective view of the cage according to
Fig. 1 wherein the support is partly withdrawn from the
outer wall,

Fig. 3

is a section along line III-III of Fig. 1,

Fig. 4

is a schematic perspective view of a part of the support
as seen in Fig. 3,

Fig. 5

is a plan view of a further embodiment of the invention,

Fig. 6

is a cross-section along line VI-VI of Fig. 5,

Fig. 7

is a schematic perspective view of a cage according to a
further embodiment of the invention,

Fig. 8

is a schematic perspective view of a cage according to a
further embodiment of the invention and

Fig. 9

illustrates the orientation of the fibers in the cage according
to Fig. 8.

[0014]

Referring now to the drawings wherein like numerals indicate
like parts, the cage of this invention is depicted by the numeral
1. The cage 1 has a pair of front surfaces 13 and 14, an
outer surface 3 and an inner surface 15. A cylindrical outer
wall 2 has several perforations or ports 4 which connect the
outer surface with the cavity and which enable fusion of bone
through the cage. Further, the outer surface 3 is provided with
a thread 8. The cage is packed with bone chips or bone substitute
not shown in the drawing.

[0015]

A support 6 having the shape of a plate is inserted into grooves
9 of the cavity 5. The support 6 is inserted in the longitudinal
direction of the outer wall 2, as indicated with arrow 7. The
outer wall 2 as well as the support are made from carbon fiber
composite. Fibers 10 and 11 are preferably oblique to the longitudinal
direction but may also be perpendicular to the longitudinal
direction. In Fig. 4 the longitudinal direction is indicated
with line 16. Fibers 10 and 11 within the support have
preferably two directions of orientation as shown in Fig. 4 and
can run along the entire length of the support 6. The matrix of
the support 6 as well as the outer wall 2 are made from PEEK or
PEKEKK preferably from commercially available Osta-PEK ®.

[0016]

Long fibers in the support 6 can extent completely along the axe
of the part that provides optimal strength and regularity of the
mechanical properties of the implant. The same is there on the
concentric fibers. These can wind up around the cylinder several
times within the part and opposing fibers can cross the entire
part in a different direction. Cross direction holds the part
together and allowing it to resist loads that will be subject
to the implant from different directions. The difference in mechanical
properties between short carbon fiber composite and
long fiber composite in a controlled orientation can be compared
to particle board and the structure in well carpentered oak.
Particle board is held together by glue, while the oak structure
uses fabric orientation of wood to oppose the forces and subjected
upon the structure.

[0017]

Fibers 12 and 17 within the outer wall 2 are preferably concentrically
and/or longitudinally oriented. The fibers 12 are preferably
long fibers and may run along the entire circumference of
the outer wall. The fibers 17 are as well preferably long fibers
and may run in the longitudinal direction along the entire
length. It is an important aspect of the invention, that the fibers
10 and 11 of the support 6 and the fibers 12 of the outer
wall 2 have different orientations. The additional orientation
of the fibers 10 and 11 prevents deformation of the cage 1 to
where the fibers 12 are bent beyond the point of failure. The
fibers 12 need not always be concentrically oriented and could
be also parallel to the longitudinal direction 16. Furthermore,
art part of the fibers could be concentrically oriented and another
part of the fibers could be parallel to the longitudinal
direction 16.

[0018]

Figures 5 and 6 disclose a cage 20 having a wall 24 with a generally
round cross-section and a support 23 integrally connected
to the wall 24. The cage 20 is formed of radiolucent material
and contains imbedded long reinforcing fibers 21 and 22. The fibers
21 of the wall 24 are generally concentrically oriented or
parallel to the longitudinal direction 16. The fibers 22 of the
support 6 have at least one additional orientation, that is
preferably oblique to the longitudinal direction 16. As shown in
Fig. 6, Fibers 22a may have an orientation different to that of
fibers 22b. Fibers 22 could be also perpendicular to the longitudinal
direction 16.

[0019]

Fig. 7 shows a cage 30, that is also formed of radiolucent material
and contains fibers 31 and 37 with different orientations.
The cage is made of two parts, an outer wall 39 having a generally
round or oval cross-section and a box-like support 33, that
slides in the wall 39 like a drawer. Apertures 34 within the
support 33 provide for bone growth and can be preloaded with
bone material. The wall 39 can also have not shown apertures for
bone growth and a thread as a part of an external surface 36.
The fibers 31 are preferably oriented in concentric circles
whereas the fibers 37 have an additional orientation, for example
perpendicular to the longitudinal direction 16.

[0020]

Fig. 8 shows a cage 40, that is also made of two parts, an outer
wall 42 and a support 43, that is an insert and contains fibers
45 and 46 having different orientations. The outer wall 42 contains
concentrically oriented fibers 41 and has a generally
round or oval cross-section. The support 43 is provided with apertures
44 which can be preloaded with bone material and slides
in the outer wall 42 like a drawer, as indicated with arrow 48.
The fibers 45 and 46 are preferably long carbon fibers and have
different orientations to each other and to the fibers 41. The
fibers 45 are vertically oriented and the fibers 46 are horizontally
oriented and parallel to the longitudinal direction 16. In
Fig. 9 the orientations of the fibers 41, 45 and 46 are schematically
indicated with arrows 47 to 49.

Claims (9)

Three-dimensional fiber reinforced implant, particularly a
vertebral cage designed to be inserted between two adjacent
vertebrae, the implant having an outer wall with a general
cylindrical or oval shape and preferably an open volume for
bone filling, said wall having reinforcing fibers which at
least in part are oriented in a first direction, a support
extending within said volume having reinforcing fibers which
are at least in part oriented in a second direction, said
first and said second directions are different.

Implant according to claim 1, wherein the fibers of the outer
wall are at least partly concentrically oriented.

Implant according to claim 1 or 2, wherein the fibers of the
outer wall are at least partly parallel oriented.

Implant according to claim 1 or 2, wherein the fibers of the
support are at least partly parallel oriented.

Implant according to any of the claims 1 to 4, wherein the
support is a separate insert.

Implant according to any of the claims 1 to 5, wherein the
support is a strut.

Implant according to any of the claims 1 to 6, wherein the
support is like a drawer inserted within said volume.

Implant according to claim 7, wherein the support is like a
round drawer.

Implant according to any of the claims 1 to 8, wherein the
fibers of said outer wall are at least partly concentrically
and the fibers of the support are at least partly longitudinally
oriented.

Cited By (1)

Placeholder for implantation to the human vertebrae has three tubular bodies having different lengths and diameters that are inserted and connected to each other by pins so that they project over the edges of the next larger tubular body

Cited By (3)

Placeholder for implantation to the human vertebrae has three tubular bodies having different lengths and diameters that are inserted and connected to each other by pins so that they project over the edges of the next larger tubular body